Fast coagulation

Due to existence of an isothermal region, temperature of both entrance and outlet was rather lower than that of intermediate section. Where temperature was high, the reaction was sever and fast. So, at site 200-300 mm away from entrance, the temperature was highest, the scale layer was thickest and the whisker column was longest there. The reaction route in this zone could be described as phase reaction homogeneous nucleation — coagulation. When... 

Here we consider aggregation in a physically realizable chaotic flow, the journal bearing flow or the vortex mixing flow described earlier. The computations mimic fast coagulation particles seeded in the flow are convected passively and aggregate upon contact. In this example the clusters retain a spherical structure and the capture radius is independent of the cluster size. 

The polymer radius has to be larger than 80% of the particle radius to avoid adsorption limitation under orthokinetic conditions. As a rule of thumb a particle diameter of about 1 pm marks the transition between perikinetic and orthokinetic coagulation (and flocculation). The effective size of a polymeric flocculant must clearly be very large to avoid adsorption limitation. However, if the polymer is sufficiently small, the Brownian diffusion rate may be fast enough to prevent adsorption limitation. For example, if the particle radius is 0.535 pm and the shear rate is 1800 s-, then tAp due to Brownian motion will be shorter than t 0 for r < 0.001, i.e., for a polymer with a... 

Wet spinning. This technique is characterized by spinning a filtered viscous polymer mass, dissolved in a suitable solvent, into contact with a precipitation or coagulation bath. Polyacrylonitrile, polyvinyl acetate, cellulose acetate, and other materials are processed by this method. Thermal requirements for pigments are less stringent than for melt spinning but pigments are expected to be fast to the solvents and chemicals used. 

Equation 7.20 with respect to Vmax is involved, and will be not discussed here. It is, however, readily appreciated that, when the electrolyte concentration is increased, the magnitude of k in the exponent of Vel also increases (compression of diffuse layers), so that the maximum caused by it becomes lower. At a certain value of C, the curve V(h) will become similar to curve b in Figure 7.8 with Vmax = 0. In accordance with all that has been said before, coagulation will become fast starting from this concentration. This is therefore the critical concentration, Ccc. In other words, the critical concentration (Ccc) can be estimated from simultaneous solution of following ... 

W is the stability ratio, i. e. the factor by which the coagulation velocity is reduced due to interparticle repulsion. It is related to the height of the energy barrier. When coagulation is fast, W = 1. Various aspects of slow coagulation are still not fully understood (O Melia, 1987). Several theories of the kinetics of coagulation are discussed by Grand et al. (2001). 

Lichtenfeld, H. Knapochinsky, L. Sonntag, H. Shilov, V. (1995) Fast coagulation of nearby spherical ferric oxide particles. Part I. Formation and decomposition of aggregates experimental estimation of velodty constants. Colloids Surfaces A. 104 313... 

Table 9.10 shows an estimate (Pandis et al., 1995) of the time scales for coagulation of smaller particles onto larger ones characteristic of various types of air masses. For comparison, typical time scales for condensation, dry deposition of the particles, and transport are also shown. (For discussions of dry deposition of particles, see, for example, Slinn (1982, 1993), Arimoto et al. (1987), and Main and Friedlander (1990)). As expected, condensation is fast, but coagulation is also significant on these time scales in some situations. 

The stability ratio W is defined as the ratio of the rate of fast coagulation to that of slow coagulation and is given by... 

Coumarins are competitive inhibitors of vitamin K, which is required for the formation in the liver of the amino acid, gamma-carboxyglutamic acid. This is necessary for the synthesis of prothrombin and factors VII, IX and X (Figure 17.1). After starting treatment the anticoagulant effect is delayed until the concentration of normal coagulation factors falls (36-72 h). The effects can be reversed by vitamin K (slow maximum effect only after 3-6 h) or by whole blood or plasma (fast). Gut bacteria synthesise vitamin K and thus are an important source of this vitamin. Consequently, antibiotics can cause excessive prolongation of the prothrombin time in patients otherwise adequately controlled on warfarin. 

A minimum volume of 400 pi plasma is required. Ethylenediaminetetraacetic acid (EDTA) blood, collected after overnight fasting, is separated within 30 min by centrifugation at 2000 xg for 10 min at 4°C. If separation cannot be performed within 30 min, blood can be kept on ice for a maximum of 1 h. Plasma is stored frozen at -20°C until analysis. Hey is stable in plasma at room temperature for 24 h, at 4°C for 1 week and at -20°C for many years. Serum should not be used, since allowing blood to coagulate leads to a delay in centrifugation. 

The new Chapter 13 collects the material on colloid stability previously distributed between old Chapters 11 and 12 and integrates it with new material on stability ratio and slow and fast coagulation, polymer-induced forces, and polymerinduced stabilization and destabilization. 

Paper and textile production retention, coagulation, flocculation, wet strength, dry strength improvement, dewatering, color fastness, dye fixation, antistatic agents, antimicrobial treatment... 

In 1965 Dunn and Taylor confirmed the theory for vinyl acetate polymerization (15), and proposed, in the light of the presumed importance of rapid coagulation during the earliest stages of reaction, that the "DLVO" theory for colloid stability (16) be applied. Fitch proposed a kinetic basis for a quantitative theory and observed that for observation of particle formation kinetics, "fast" reaction techniques must be used because "particle formation occurs in a matter of seconds or even less (17)". 

The so-called "Smoluchowski fast coagulation rate" may be characterized by a half-life independent of particle size (36) ... 

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